Josh van der Flier is set to miss the rest of Leinster's season with Robbie Henshaw also a big doubt for Saturday's European Champions Cup quarter-final against Ulster.
Flanker van der Flier has undergone surgery on a groin injury he picked up in Ireland's Six Nations win over France earlier this month.
"Josh is likely to miss the rest of the season," said Leinster boss Leo Cullen.
Cullen added Henshaw is "less likely than likely" to feature on Saturday.
Henshaw has not played since starting at full-back for Ireland in the opening Six Nations defeat by England.
The former Connacht centre has resumed training after his leg injury took longer to heal than was initially expected.
"Whatever way the tear in the muscle was... the dead leg was initially what the cause of concern was but there was a little bit more damage a bit deeper in," added Cullen, who revealed that Henshaw visited a specialist in the UK.
"So it was a little bit unusual, probably, from initially the way it presented, obviously as a dead leg.
"He had a little minor procedure done but I couldn't get into the technicalities of that."
Hooker Sean Cronin and centre Noel Reid are undergoing return to play protocols after sustaining head injuries in Friday's Pro14 defeat by Glasgow.
Ulster are expected to provide an update on Tuesday on the fitness of Louis Ludik, Darren Cave and Marty Moore who all had to leave the field early in Saturday's win over Southern Kings.
Ludik suffered a leg injury with Cave taking a bang on the ribs and Moore sustaining a knock to the head in Saturday's game.
Iain Henderson is already involved in a fitness battle for the game after sustaining a sprained knee in Ireland's penultimate Six Nations game against France.
Another Ireland squad member Will Addison is expected to miss the European quarter-final because of the back injury which has kept him out since January.
The doubts over Cave's availability mean that Ireland centre Luke Marshall could be in line for an earlier than expected return to duty after not playing since last May because of a cruciate ligament injury.